This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We have constructed a novel simian-human immunodeficiency virus (SHIV), a hybrid virus that is part monkey AIDS virus (termed SIV), part human AIDS virus (termed HIV-1). This hybrid virus, SHIV-Bo159N4, encodes the envelope gene of a primary HIV-1 strain that was adapted in human brain-derived cells. Our new virus, SHIV-Bo159N4, replicated well in blood cells of all monkeys tested. Like the original HIV-1 strain from which we derived the envelope gene, our SHIV-Bo159N4 enters cells through a molecule called CCR5. Cells infected with our new virus form giant cells that contain many nuclei. To test whether SHIV-Bo159N4 can replicate in vivo, rhesus monkeys were inoculated intravenously and mucosally with this new virus;all had high viral RNA loads. To increase viremia in the acute phase, the CD8+ cells were depleted in some animals shortly after inoculation;high viral RNA levels were seen in plasma and cerebrospinal fluid (CSF). We have also inoculated pigtailed monkeys with SHIV-Bo159N4 under depletion of CD8+ cells;again, very high viral loads were observed in plasma and CSF. The animals with the highest CSF viral RNA loads were euthanized, microglia were isolated and transferred to new recipients. Brain sections are being tested for evidence of productive viral infection and brain disease. We are currently following 10 rhesus and 2 pigtailed monkeys with chronic infection for the development of disease. We have also constructed a second new SHIV that encodes the envelope gene of an African HIV-1 strain that is a genetic subtype (or Clade) A strain. This new Clade A SHIV is called SHIV-KNH1144. We are now in the process of adapting this new SHIV to replicate to high levels in rhesus monkeys. Two rhesus monkeys have already become systemically infected.